Currently the most accurate method of visually inspecting laser drilled holes comprises placing a light source at one side of a component through which a hole has been laser drilled and providing a camera at the opposite side of the component. This is known as “backlighting” the hole. Backlighting the hole provides good contrast between the hole and the component and enables the use of edge detection software to determine the edge of the hole in the component. The camera is arranged to view the laser drilled hole and an associated computer with edge detection software determines if the laser drilled hole conforms to the required position, dimensions and shape etc. However, this method of visually inspecting a laser drilled hole is performed “offline” after the hole has been drilled. If the laser drilled hole does not conform to the requirements, it is necessary to re-drill the hole in the component such that it conforms to the requirements.
Conventionally components with a plurality of laser drilled cooling holes are inspected many times during the manufacturing process and this involves stopping the laser drilling process to measure the position, dimensions and shape of the cooling holes to ensure that they conform to the requirements.
There is requirement to inspect the laser drilled holes “online” during the laser drilling process and to correct the laser drilled holes as they are produced via a feedback loop. This would be advantageous because it would avoid the need to stop the laser drilling process for manual inspection, increase productivity, reduce the scrap rate and avoid the need for re-drilling.
In order to inspect the laser drilled holes “online” or “in-process” it is necessary to provide “backlighting” for the camera to view the component because this type of illumination provides the most accurate edge detection for the laser drilled hole.
However, there is a problem if “backlighting” is used to illuminate the component and the laser drilled hole in the component because the light source is in the direct path of the laser beam. The use of “backlighting” has two significant disadvantages. Firstly the dross, dust, spatter, e.g. the molten material droplets and/or molten material droplets which have cooled and solidified, produced by the laser drilling through the component quickly collects on the light source thereby reducing the light output from the light source and hence makes the comparative measurements extremely difficult. Secondly the laser beam directly strikes the light source once it has drilled through the component which heats the light source thereby leading to degradation and eventual failure of the light source.
Therefore the present invention seeks to provide a novel apparatus and method of machining a shape through a component, which reduces or overcomes the above mentioned problem.